Secondary multiplication power tube



-.July 23, 1946. A. VARELA SECONDARY MULTIPLIGATION POWER TUBE Filed 001; 13, 1941 5 Sheets-Sheet 1 400 800 PRIMARY ELECTRON VOLTS Arllull' A. Varela Y R v a m w R m m a T L V T 0 N V l A F r W B l 7 1 V v a c July 23,1946. A. A. VARELA 2,404,417

SECONDARY MULTIPLICATION POWER TUBE Filed 001;. 15, 1941 3 Sheets-Sheet 2 ILE- INVENTOR Arm A Varela nifomvsr; 7

SECONDARY MULTIPLICATION POWER TUBE Filed Oct. 13, 1941 s Sheets-Sheet 5 I II Patented July 23, 1946 Arthur A. Varela, Washington, D. 0. Application October 13, 1941, Serial No. 414,771

9 Claims. (01. 250-27) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) In intermittent service at high power levels where operation occurs for very short intervals and during a small percentage ofthe time, a thermionic emitter in ultra high frequency power tubes presents a severe limitation by reason of its necessary large size and high heat dissipation. It also greatly reduces the overall efficiency because continuous heating of the emitter is necessary.

It is a purpose of this invention to provide electronic power amplifiers and oscillation generators for ultra high frequency operation at very high power levels wherein the electronic current is obtained by bombardment and. secondary multiplication. In this manner the electron source is operative only during operating periods of the tube so that full advantage is taken of intermittube;

Fig. 4 is a diagrammatic representationof .a second form of tube embodying the invention together with its accompanying circuits;

Fig. 5 is a graph similar to that of Fig. 3 but having reference to the tube of Fig. 4;

Fig. 6 is a diagrammatic representation of a tube constituting a third embodiment of the invention together with the accompanying circuits;

Fig. '7 is a view of a fragment of a tube shown in Fig. 6; g

Fig. 8 is a diagrammatic representation of a tube constituting a fourthembodiment of the invention together with its accompanying circuits;

Figs. 9, 10 and 11 are sectional views of various forms of electrodes which are preferred for use in the tubes illustrated in thepreceding figures, and

Fig. 12 is a diagrammatic representation of a portion of the serrated emitting surface of the electrode shown in Fig. 11. I

When certain materials are bombarded by electrons the release. of secondary electrons from the material results. The number of secondary electrons thus released depends upon the velocity of the bombarding electrons and has a general funce tion as shown in Fig. 1 wherein the ordinate o" is the ratio of the secondaries released to the primaries arriving and the abscissa is the voltage of arrival of the primary electrons. It will be necessary that the ratio increases linearly with the primary voltage up to about-400 volts after which the rate of increase decreases until the ratio becomes substantially constant. The maximum ratio may be as high as 10. In the'tubes constructed according to the invention'and described hereinafter this phenomenon is employed to obtain modulated electron currents of high density by shuttling the electrons back and forth between two electrodes having high secondary emissivity in such mannerthat multiplication is obtained during each collision cycle.

In the tubes shown in Fig. 2 reference character I indicates a disk electrode having its surface treated for high secondary emission. Reference the shape of a disk as shown and of such size as i x to exceedthe lateral dimensions of 4. An evacuated glass envelope 6 encloses the electrodes. The cylinders 2 and 3 may either be outside the envelope as shown or may beenolosed in it. Solenoids 1 and 1' provide amagnetic field which is coaxial with the tube. 7 ground; cylinder 2 is connected to an-R. F. tuned circuit 8; cylinder 3 and electrode 4 are at R. F. ground and electrode 5 is connected to an R; F. tuned circuit 9 which is regeneratively coupled to the circuit 8. D. C. potentials are applied by source I0 such that cylinders 2 and 3 are rendered positive relative to electrode! and electrodes 4 and 5 are further positive; The-solenoids l and 1' are disposed so that the magnetic field bends out in the neighborhood of'4.' The operation of this tube is as follows: 1

It will be seen that an R. F. field exists betweenelectrode l and the end'of cylinder 2 and between cylinder 3 and the other end of 2. Potentials and spacing are made such that the electron transit time from a to b is approximately andthe sum of the transit times from b to c and that of the secondary electrons-from c to b. is approximately Electrons leaving the electrode I Electrode I is at 3.1.

3 when the R. -F. field is zero and becoming negative will arrive at b when the field here is maximum with a positive accelerating polarity.

These electrons will then arrive at electrode 4 with a net velocity equal to the peak R. F. voltage of cylinderl. These electrons will then re-' lease a number of secondary electrons from electrode i which will travel back down the tube toward I. ,They will arrive in field b 180 after the passage of the primary electrons and hence this field will again be maximum and with a positive; accelerating polarity. The field at a will be passing through zero upon the arrival of the electrons at I while at the same time the R. F. voltageat 2 will be at its peak. New secondaries will be released from I and these will repeat the cycle. Since this multiplication process is sustained current densities may rapidly build up to very high values. The multiplication cycle as just described is indicated graphically at Fig. 3. It will be necessary that the electrons considered bear the optimum phase relation for sustained multiedges of 4 and will attract electrons coming intoit. {This combined with the curvature of the magnetic field in the vicinity of 4 will cause secondaries from the outer portion of A to go to 5; Secondary electrons leaving 4 will be much more susceptible to the field of 5 than will the oncoming primaries because the secondaries leave with virtually zero velocity'and are readily deflected Whereas the primaries approach with relatively very high velocity and are not so readily defiect ed} 'I-Ience a considerably greater current may arrive at i than will pass down the tube from it The excess electrons which equal times the our rent arriving, minus the current returning down the tube, then flow to the anode 5. Because of the high D. Clpotential of the electron current adjacent these disks are located steady potential cylinders 2 and 2 while between these cylinders is located the R. F. accelerating cylinder 3. Behind the emitter disks are located screen grids II and II respectively and behind the grids are located collector electrodes5 and 5. T An evacuated glass envelope may or may not enclose the cylinders. A series of 4 focusing solenoids l are located outside the envelope coaxialar therewith.

' cuit angles of the fast electrons from b to a and from. b. to a plus the circuit angles of the 1 slower electrons from a to b and from a to b is equal to 180. Passage of an electron having maximum bombarding potential is indicated by the dotted line in Fig. 5. It receives acceleration bothrat b and at b and arrives at a with a velocity equivalent to twice the peak R. F. voltage on 3, sustained multiplication taking place as before. Again electrons in other phase relations will arrive with lower velocities or will not arrive at all. Hencethe electronic current will be completely modulated. All current beyond the value which can be maintained in focus by the magnetic field will be drawn by the electric field of H, II and will pass through these grids to 5 or 5 respectively. Assuming a multiplication ratio of 6 then the current flowing to anodes 5, 5' will be five times the current flowing down the tube. Since the anodes 5, 5" may have much higher R. F. swings than does 3, the power gained may be very high. y

The embodiments described above are adaptable to operation at frequencies of 600 megacycles or less. For higher frequencies it is preferred to employ confined field resonators (resonant cavities) A tube of this type embodying the invention is shown in Fig. 6. Referring to this figure a secondary emitter disk I is shown positioned at one end of the tube with the secondary emitter electrode 4 positioned in the opposite end and preferably in the form of a truncated cone as be made to pass to it when its radio frequency voltage is negative and hence may generate R. F. power. The power inputto 8 may be taken asequaito the a. F. voltage of cylinder 2 times the current it accelerates. Likewise the power output of 5 may be taken as the current flowing to'it times its R.F. voltage. Neglecting harmonic components this is true because the current modulation iscomplete and no steady current flows. It is evident that the power'output may be many times the driving power and hence oscillation 1 canbe obtained. Themaximum R. F. swing of electrode 2 should be limited to about 600 volts peak.

Beyond this harmonic generation increases rapidly. The miximum R. F. swing of 5 will be limited solely by the applied D. C. potenv tialJ The current values will be determined by the strength of the magnetic field. 'Modulation of the output may be had by varying the potential of cylinders -2 or 3 or both. I

I'he embodiment illustrated in Fig; 4 constitutesfa double ended variation of the tube of Fig. Zfw-hich may give somewhat higher efficiency. The secondary emitter disks I and I 'are'located in th e oppOsite ends of thetube. Immediately shown. Behind the electrode 4 isa grid II preferably composed of radial wires as shown in detail in Fig. '7. Behind the grid is located the collector anode I2 which is preferably in the shape of a closed cylinder asshown. An evacuated glass envelope 6 encloses these elements. A confined .field resonator I3 surrounds the end of the tube adjacent the emitter disk I while a similar confined field resonator surrcunds the collector anode I2 and aportion of the glass envelope ad: jacent thereto. D. C. insulation is provided at I5. Focusing solenoids I are employed as before. Regeneration coupling loops I6 are employed in connection with resonance cavities I3 and I4 to obtain oscillation.- The load is removed by means of a coupling loop H. A source of D. C. potential I0 is employed as before. An electric R. F. field is produced in gap I8 by resonator I3. The sum of the fast and slow transit angles from I8 to i and back is The same is true from I8- to d and back. Hence the electrons leaving I or 4 in I are removed from 4 by the field of grid II and 7 passed through II to collector anode l2 when I2 is atynegative R. F, potential. As is the case with the embodiment shown in Fig. 2, due to the shape of 4 and the contour of the magnetic field surrounding it, a greater density of electrons may arrive at 4 than can be held in focus when moving in the opposite direction. Hence a uni-lateral effect is obtained with a majority of electrons moVing from right to left as illustrated, striking electrode 4 and a smaller number mOVing through the tube from left to right.

In the embodiment shown in Fig. 8 two symmetrical accelerating fields 180 apart are employed. This results in two space charge clouds moving in opposite direction. Collisionv of these clouds occurs in the center producing a high space charge densit here so that the desired excess of electrons passes through a cylinder gridl l t the outer cylindrical anode l 2. The R, F. field of the output cavity I9 is shielded from the main beam by the cylinder grid H;

Focusing may be accomplished as before by the use of a magnetic field but electric focusing is shown in Fig, 8. This type of focusing is obtained by the use of parabolic or concave-shaped emitter electrodes 4 and 4. The field (equal potential lines) then follows this contour near the surface and the slow electrons comingofi are directed toward the focal point. 1 They are not. greatly afiected bythe subsequent defocusin fields be cause of their high velocity. The symmetrical accelerating fields are. produced by means of confined field resonators. l3 and I4. These resonators produce accelerating fields at 18 and IS". The cavities .of resonators l3 and I4 are, coupled to the anode cavity l9 by means of loops 20. An. evacuated glass envelope 6 encloses the elements of the tube. Loop' I1 is provided for removingthe load. D. C. potential is supplied bysource-Hl. Circuit angles between I8 and 4' and those between IB and the center of the tube and between I8 and the center of the tube are indicated in the upper portion of the illustration.

Electric focusing as shown in Fig. 8 may be employed in any of the embodiments described and should be satisfactory for steady operation where space charge. densities do not run high. For

pulsing operation a combination of electric and magnetic focusing is-probably desirable. If electric focusing were employed in the embodiment of Fig. 2 the electrodes .would be made in the shapes shown in Fig. 9. If employed in the embodiment illustrated in Fig. 4 the electrodes would be as shown in Fig. 10. If employed in the embodiment illustrated in Fig. 6 the electrodes would be as shown in Fig. 9.

Since the maximum number of secondaries is produced when primary incidence is about 70 corrugations in the face of the secondary emitters illustrated above are desirable and these may take the form illustrated in Fig. 11. Fig, 12 shows on a large scale a fragment of the surface of Fig. 11 illustratingthe correct angular relationship of the faces.

, The invention described herein may be manufactured and used by or for the Government of which is greater, than unity, a pair of cylindrical coilssurrounding a line passing through the centers of'said emitter electrodes, said coils being longitudinally spaced along said line and coaxial therewith, means impressing a potential on said coils whereby a magnetic field is formed along said line confining the flow of electrons between said electrodes to a path coaxial with said line, a confined field resonator surrounding a portion of said path and having an annular gap surrounding the portion of said path lying between said coils, and means producing radio frequency,

oscillations in said resonator, whereby a radio frequency field is formed in and around said gap, the characteristics of said field and the dimensions of said path being such that the transit angle with respect to said radio frequency of an electron travelling said path from said field to one of said electrodes plus the transit angle from said electrode to said field of an electron emitted by impact of said first mentioned electron upon said electrode, is 180.

2. An electron discharge device comprising'an evacuated envelope, a pair of emitter electrodes contained therein and spaced from each other, 'said electrodes having facing surfaces capable,

upon impact by electrons, of emitting secondary electrons at a ratio to saidimpacting electrons which is greater than unity, a pair of cylindrical coils surrounding a line passing through the centers of said emitter electrodes, said coils being) longitudinally spaced along said line and coaxial therewith, means impressing apotential on said coils whereby a magnetic field is formed alongsaid line confining the flow of electronsbetween radio frequency oscillations in said resonator,

whereby a radio frequency field is formed in and around said gap, the characteristics of said field and the dimensions of said path being such that the transit angle with respect to said radio frequency of an electron travelling said path fromsaid field to one of said electrodes plus the transit angle from said electrode to said field of an electron emitted by impact of said first mentioned electron upon said electrode, is 180.

3. An electron dischargedevice comprising an evacuated envelope, a pair of emitter electrodes contained therein and spaced from each other, said electrodes having facing surfaces capable,

' upon impact by electrons, of emitting secondary longitudinally spaced along said line and coaxial electrons at a ratio to said impacting electrons which is greater than unity, a pair of cylindrical coils surrounding a line passing through the centers of said emitter electrodes, said coils being therewith, means impressing a potential on said coils whereby a magnetic field is formed along said line confining the flow of electrons between said electrodes to a path coaxial-with said line,

said coils being so located as to shield the portions of said path surrounded thereby from radio frequency fields, a confined field resonator surrounding a portion of said pathand'having .an

- annular gap surrounding the portion of said path lying between said coils, said resonator being so formed and located as to shield a portion of said path from radio frequency fields, and means producing radio frequency oscillations in said ress onator; whereby a radio frequency field is formedv contained therein and spaced from each other, said. electrodes having, facing surfaces capable,1 upon impact by electrons, of emitting secondary electrons at a ratio to said impacting electrons which is greater than unity, a pairi of cylindrical coils surrounding a line passingthrough the centers of said. emitter electrodes, said cells being longitudinally spaced along said line and coaxial therewith, means impressing a potential on said coils whereby a magnetic field is formed along said li-ne confining the flowof electrons between saidelectrodesto a path coaxial} with said line, a confined field resonator surrounding a portion of said path and having-anannular' gap surrounding the portion of said path lying between said c'oi-ls, means producing radio frequency oscillations-in said resonator, whereby a radio fro quency field is'formed in and around said gap,

the characteristics of said field and the dimen-,

sions of 1 saidpath being such that the transit angle with respect to said radio frequency of an electrontravelling said path from said field to one of said electrodes plus the transit angle from i said electrode to said field of an electron emitted by impact of' said first mentioned electron upon said electrode, is 180 and means to collect a portion of the electrons travelling said path.

5. An electron discharge device comprising an said' electrodes having facing surfaces capable, upon impact by electrons, ofemitting secondary electrons at a ratio to said impacting electrons which is greater than unity, a pair of cylindrical coils surrounding a linepassing through the centers of said emitter electrodes, said coils being longitudinally space along said line and coaxial therewith, means impressing apotential on said coils whereby a magnetic field is formed along said line confining the flow of electrons between said electrodes to a pathncoa-Xial with said line, a' first confined field resonator surrounding a portion of said path and having an annular gap surrounding the portion of said path lying between said coils; a second confined field resonator surrounding a portion of said. envelope, a collector electrode enclosed i'n'sai'd' second resonator and extending within said envelope adjacent one of said emitter electrodes, means producing synchrol nize'd radio frequency oscillations in said reso nators, whereby a radio frequency field is set up alongsaid path adjacent-"said gapand between said collector electrode and the one of said emitter electrodes adjacent thereto; the characteristics of said'fi'e'ld adjacent said gap and the dimensions j of said path being such'that the transit angle with respect to said radio frequency of an electron travelling said pathfromsaid field to one of'said electrodes plus the transit angle from said electrod'e'to said field of an electron emitted by impact ofs aid first mentioned electronupon said electrode, is 180 whereby secondary multiplication will he maintained in said device-and a por- 34c evacuated envelope}a pair of emitter electrodes contained thereiii: and spaced from each other,

tion of the electrons travelling. in said path. will be: collected; by- Said collector electrode.

6. An..electron. discharge devicezcomprisingan' evacuated envelope, a pair of emitter electrodes contained therein and spaced from each other,

said electrodes" having. facing surfaces capable, upon impact by electrons, of emitting. secondary electrons at ,a ratio' to said impacting electrons which is greater than unity, a pair of cylindrical coils surrounding a line passing through the centers of said. emitter electrodes, said coils being longitudinally spaced along said line and coaxial therewith, means impressinga potential on .said

coils whereby a magnetic field is formed along said line confining the flow of electrons between said electrodes to a path coaxial with said line, a first confined field resonator surrounding a portion of said path and having an annular gap surrounding the portion of said path lying between said coils, a second confined field resonator surrounding a portion of said envelope, a collector electrode enclosed in saidsecond resonator and extending within said envelope'adjac'ent one of said emitter electrodes, means producing synchronized radio frequency oscillations in said resonators, whereby a radio frequency-field is set upalong said path adjacent said gap and between said collector electrode and the one of 'said emitter electrodes adjacent thereto, a grid positioned-between said collector electrode and said one of said emitter electrodes means, said grid being maintained at a positive potential with respect to said one of said emitter electrodes and said collector electrode being'maintained" at a positive potential with respectto said grid, the characteristics of said field adjacent said gap and the dimensions of saidpath being such that the transit plication will be maintained in said device and a portion of. the electrons travellin in said path will be collected by said collector electrode.

7-. An electron discharge'device comprising an evacuated envelope; a pair of emitter electrodes contained therein and spaced from each other, said electrodes having facing surfaces capable upon impact by electrons, of emitting secondary electrons at a ratio to said impacting electrons whichis greater than unity, means causing electronstravelling between said electrodes to follow a prescribed path, a pair of confined field resonators surrounding portions of said path and coaxial therewith, saidv resonators being so located as to shield portions'of said. path; ,each'of said-resonators having an annular gap formed therein and surrounding said path, a tl' n'rd confined field resonator positioned between saidfirst two resonators and insulated therefrom, said third resonator being coaxial with said path, and! the third resonator, having an annular gap formed therein,' 7

said gap surrounding said path, and being located at the center thereof, a cylindrical grid positioned in said gap, means coupling saidv resonators-said first mentioned gaps being symmetrically located with respect to the center of said path, the d'imensions of "said; resonators being such that the transit angle with respect to'sai'd' radio frequency of an'electron travellingin said path from one of the first two of said gaps to the adjacent one' of said emitter electrodes; plus the transit'angle with respect to said radio-frequency from said 9 e'ectrodes to said field of an electron emitted by impact of said first mentioned electron on said electrode, is 180 and the transit angle of an electron travelling between said fields is 180.

8. An electron discharge device comprising an evacuated envelope, 9, pair of emitter electrodes contained therein and spaced from each other, said electrodes having facing surfaces capable upon impact by electrons, of emitting secondary electrons at a ratio to said impacting electrons which is greater than unity, means causing electrons travelling between said electrodes to follow a prescribed path, a pair of confined field resonators surrounding portions of said path and coaxial therewith, said resonators being so located as to shield portions of said path, each of said resonators having an annular gap formed therein and surrounding said path, means shieldingsaid path between said resonators, means coupling said resonators, the location of said gaps being such that the fields formed in and around each during the oscillations of said resonators will periodically accelerate the flow of electrons from the adjacent one of said emitter electrodes toward the center of said'path, the coupling between said resonators being such that said periods of acceleration of electrons travelling from each of said electrodes toward the center of said path will occur simultaneously, and means to collect a portion of said electrons at the center of said path.

9. An electron discharge device comprising an evacuated envelope, a pair of emitter electrodes contained therein and spaced from each other, said electrodes having facing surfaces capable, upon impact by electrons, of emitting secondary electrons at a ratio to said impacting electrons which is greater than unity, means causing elec trons travelling between said electrodes to follow a prescribed path, means establishing a pair of synchronized radio frequency fields along said path, said fields being symmetrically located with respect to the center of said path, means shielding the remainder of said path against the occurrence of radio frequency potentials therealong and means to collect a portion of said electrons travelling said path, said collecting means being located at the center of said path.

ARTHUR. A. VARELA. 

